Method of making road-beds and pavements.



No Drawing.

JOHN A. JOHNSTON, QF,WORCESTER, MASSACHUSETTS.

METHOD OF MAKING ROAD-BEDS AND IPAVEIVIIENTS.

mosses,

-and practicable construction at a minimum of expense. 7

It has been proposed heretofore to apply bitumen in a molten condition to'a layer of broken stone in the manufacture of road beds for the purpose of thoroughly binding the stone together and forming a compact andlasting foundation, but there has always been some diificulty owing to the fact that the bitumen might not always flow thoroughly into all the interstices between the stones, and after it has once set it is a diiii cult matter to force it farther in by rolling. Moreover, if it fails to flow into all the interstices, it leaves voids between the stone layer and foundation which sometimes results in .large' masses of material being loosened. y The principal ob ect of this invention 15 to provide an improved method of uniting the bitumen with the entire layer of broken stone. It can be applied either to-one or more layers in the road bed. This is done according to this method by reversing a portion of the usualprocess and yet using a part of it, that is, the layer of broken stone is not all-put on the road-bed at the same time, nor is all the bitumen for a single. layer applied at once, as has been the case heretofore, but a small portion of the stone is first spread on and, Without being rolled at all, is treated with an excess of bitumen/Q This fills all the voids and runs down to the foundation below so as firmly .toun'ite therewith and at the same time provides a material amount of bitumen above this portion of the layer of stone. Then the rest of the stone layer is applied on the top of the bitumen and rolled thoroughly in place, after which the remainder of the bitumen is added to it. This double treatment with bitumen results in providing a complete filling of all the voids in the entire layer of Specification of Letters Patent. Application filed February at, 1912. Serial N0.679,691.

I stone as the molten material coming down Patented ma a, rare.

from above meet-stile bitumen previously applied and melts its surface so that the two bodies of bitumen are homogeneously united. Moreover, if there is any flaw in the application of the bitumen so that there are any voids not filled, these} must occur at the middle or about half wayibetween the upper and lower surfaces of the stone layer where they are entirely surrounded by the bitumen and broken stone conglomerate instead of being at the bottom as heretofore,

Where there is no bitumen immediately -below. This is an advantage because in the\ first place a void occurring at this'point is only a short distance from the upper surface of bitumen, and consequently it cannot be of as great an extent as when it occurs at the bottom at a greater distance from the upper layer of molten material. Moreover, the old method permitted at times a comparatively wide space between the foundation and broken stone layer unfilled with bitumen, this providing an opportunity for a solid block of the broken stone and bitumen to crack away. It will beunderstood also that'by applying the bitumen to the lower part of the layer of broken stone, and thereafter applying the rest of the layer of stone and rolling it in, the bitumen is forced up into the second layer of stone a material distancehy the rolling process and that at this point the upper portion of the stone is thoroughly forced into the bitumen by the heavy pressure of the roller. Another advantage of' this method is that the bitumen is prevented by the broken stone to which it is applied from flowing ion the cambered surface or getting into an luneven condition so that the rest of the stone is applied on a uniform layer of bitumen.

Having described the invention broadly, I will now describe a specific pracjzlical'way of carrying it out.

After all foundations are in place' the'sub surface is'brought to a grade 2" below; and

parallel to the proposed finished surface with a crownor camber not to exceed"=}-' per ft. of cross section. This sub-surface isthoroughly rolled. All depressions "iwhich may appear are filled and againrolled, and the rolling continued until a firm, well com pacted truesurface is obtained On the sub-grade, prepared as described, is placed broken stone, which should be not "less than 1%" 111' their longest dimensions. These are so spread, that, after thorough rolling-the 4 sprayer at the rate of J; surface and at a pressure of to pounds;

resultant surface will be '2 allel t0 the proposed finished surface of the road; all depressions formed under the rolling are filled with stone of the same size as previously used for this the rolling continued untilan surface is obtained, which must line, grade, and cross section. U11v the sur face so prepared, is spread a layer of broken unyielding stone, which vary in size from 51- to 111:"lin' per in. Over this bitumen is layer of coarse, yds. of sand per "spread: a clean. sand,-using 0.02 on. sq. yd. of surface. ()n this bituminous inatrix'is then spread suflic ientf size) to complete this stone stone (5% to 1-5 layer and to bring the surface to a point 9;" below the proposed finished surface.

The Whole then-is Watered "and rolled, until smooth, all depressions the stone surface is filled with stone of the same size as the rest of the layer, and again rolled. Only enoughrolling is done to. take out the'depressions and true up the surface, butnot enough tovclose the interstices of the stone. Care must be taken tokoep this surface absolutely free from dirt. (in thestone surface so prepared, water is sprinkled, and while still wet, there is sprayedover it a layer of bitumen, heatedtoabout 250. de-- grees, F.,.applied at the rate of if gal. per sq. yd. of surface, 70 to 80 pounds per sq. in. Over this bitumen is spread grit, (preferably stone chips, all of which should pass through a -lnoshof -1-", and none through a mesh of Only enough grit is used to prevent the bitumen from sticking to the Wheels of the roller. This surface again Wetand "another lay r of bitumen applied andcovered in the same manner as the previous one, except that more grit is used for covering. The ivholo road isthen well Watered and thoroughly rolled, using such additionalgrit as may be neiuled to cover any bitumen that appears on. the surface, and the rolling is continued until there is no movement of the road material under the roller and whole becomes tlpiroug'hl'y' compacted. 7

Although "i have described in great detail a specific way of carrying out the invcnti m,'slatiu;; relative proportions and ab-- solute measurements of the niaterialsemployed, this description is siren simply for below, and par-- layer, and

example. a be true to viding a foundation,

thin layer of broken stone, applying to the Thus it will and at the pressure of come into contact with the new carryout the method on a commercial scale, and 'l am aware that the invention is not hunted to the particular proportions or even the precise order of-steps specified 1n the Therefore 1 do not Wish to be limited to these features, but- What I do claim is r i LA method of making uniform roadways and pavements which consists in prospreading thereon a broltenstone a body of molten bitumen sufiieient to fill the voids of the broken stone and to cover the same, then applying the remainder of the layer of broken stone of the same character on the top of the bitumen and rolling it in to fore-e the upper parts of the bitumen up intothe voids inthezpart of the stone layer latest applied, and finally applying molten bitumen on the stoneto permit it to fiovv down to fill the voidstherein, and to come into contact with the first mentioned layer of bitumen A, method of making roadways and top of the pavements which. consists inproviding a hard foundation having rolled broken stone at the top, sp eading thereon a thin layer of 'unrolled broken stone, applying to the thin layeriof hrokenstone a body of molten bitumen snllieient to fill the voids and to cover the same, then, applying the remainder of the-layer of hrolcen stone on the top of the bitumen and rolling it in, applying molten bituinen onthe top of the stone to permit it to lowdown toiill the voids therein, andto come While molten into contact with the first mentioned layer ofbit nnen Whiiestill Warm, whereby the two'bodies of bitumen become homogeneously united and the entire mass becomes uniform fron'i bottom to top, and spreading a'tliin layer of grit over the topthereof.

A method of making roadays and pavements which consists in providing a foundation, spreadingthereona-thin layer of broken stone, Wetting it, applying to the broken stone a body of molten bitumen sulii-. oient to fill the voids of broken stone and to cover the same, applying alayer of coarse clean sand, then applying the remainder of the layer OllbIOlCQH stone onthe top of the bitumen and rolling it to smoothitssurface butnot sulliciently to close up the voids, wetting the stone, and finally applying molten bitumen on the top ofthe stone to permit it to flow down to fill the voids therein, and to first mentioned layer of bitumen and sand.

A method. of makingroad-Ways and pavements wvhich consists vin providing," a foundation, spreading thereon a thin layer of broken stone, spraying on the broken stone at body of heated molten bitumen under pressure, then applying the remainder In testimony whereof I have hereunto set of the layer of broken stone on the top of my hand, in the presence of two subscribing 10 the bitumen alflid rolling it to fOI'm 2LSIIIl;)Oth witnesses.

surface and nally spraying molten itumen urider such pressure on the top of the JOHN JOHNSTON stone so as to force it to flow down to fill Witnesses:

the voids therein, and to come into Contact ALBERT E. FAY,

with the first mentioned layer of bitumen. C. FORREST VVESSON. 

